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Original question:

AFE3010: Application note in 50Hz

AFE3010: Several questions

Naizeng Wang
Expert 4660 points
Part Number: AFE3010

Hi team,

I have some questions about this device. 

(1) What's the working principle of Ground to Neutral fault?

(2) The AFE3010 monitors power line signal phase at any given time through the PH and SCR_TST pins. So which pin's information is used for phase detection?

(3) SCR Integrity Test: The device induces a SCR anode signal transition with the help of SCR_TST pin. So when conducting this test, SCR_TEST drives a weak HIGH output, then SCR is fired and SCR_TEST is transformed to low. Right?

(4) When there is a leakage fault, the current in hot line is If+IL and that in neutral line is IL, so the leakage current is If. So what's the quantitative relationship between If and induced voltage? I think it should be V=N(dphi)/dt=N*L*di/dt. So the induced voltage is proportional to di/dt rather than If. Right? 

Br,

Nison

  • 0
    TI__Mastermind 31125 points

    Hello Nison,

    (1) The working principle of ground-to-neutral fault (G-N) detection is essentially Ampere's Law and that a small current induced into the line wires (HOT and NEUTRAL) will not return if there is leakage/fault from NEUTRAL to Earth Ground. So the NGOUT pin induces two large current spikes into the secondary coil a 200-turn current transformer. This induces a changing magnetic field in the core, which then induces a current into the Line wires passing through the core. If there is some leakage from NEUTRAL to Earth ground, then that induced current will not return back through the CT, thus inducing a differential current through the core, which of course in then sensed by the 1000-turn coil and generates an a current in its secondary coil, which is being sensed by AFE3010 amplifier.

    See Figures 18 and 20 for better understanding.

    (2) Both pins are actually monitoring phase zero-crossings. If either pin senses missing zero-crossings, then the watchdog-timers will sense this as a failure mode and will fire SCR and blink the ALARM.

    (3) Yes the SCRTST pin is testing/sensing the SCR integrity every ~3 seconds when the SEL pin is connected to GND.

    (4) If you are asking about the induced voltage on the OUT pin (output of the amplifier), the relationship is not based upon the rate of change of IGF (fault current), rather it is simply proportional to the value of IGF. VOUT = (IGF/N)*Gain + 2.5V, where N=1000 turns and gain ~ RFB = 36kΩ, which is the recommended value in the datasheet.

    Hope this helps.

    Best,

    Peter

  • 0 in reply to Peter Iliya
    TI__Expert 4660 points

    Hi Peter,

    Thanks for your reply. About the question (3), during SCR Integrity Test, the SCR will be fired. Right? If so, LOAD
    SWITCH will be open and system will enter power down. This test will definitely affect the normal operation of system. 

  • +1 in reply to Naizeng Wang
    TI__Mastermind 31125 points

    Hey Nison,

    Well technically the SCR nor solenoid will NOT be fired during the device automatic self tests. This situation you describe is definitely not how the device will react or else self test feature would ruin functionality. The SCR self test is I believe done during the negative cycle and while the SCR anode is driven high momentarily will, the device can sense if the SCR gate and anode voltages are moving properly, the correct transient voltage will trip the internal comparator and device will know the SCR passed the SCR self test.

    Hope this helps.

    Peter